It is not that easy to compare as the same conditions rarely apply. Axial is easy for home construction as there is no significant machining required but that does almost dictate the use of an air gap alternator. You could make a radial air gap alternator that would have similar characteristics but it is an awkward construction.
Similarly you can make an axial with slotted iron core but it an awkward thing.
Personally I think the issue comes down to your facilities, what you want to scrounge compared with what you want to buy and how much benefit you place on the lack of iron loss and hence better VERY low wind performance. I think many take this low wind bit too far and loose out but it does depend on the wind area and the type of loads that you use.
For large power machines for heating there is no point in worrying about a bit of iron loss, there is no heat in low winds but if you want to charge batteries for low winds to have light and other non heating power then that may be a different issue.
You will use less magnets for the same output with a slotted iron core and if you can scrounge the core from a scrap motor it will be cheaper. If you considered the cost of making your own stator core for a one off machine then it would be cheaper to buy some bigger magnets. Iron cored axials are not attractive as there no cores to scrounge and even without slots good core material puts the cost way up.
I have built several machines of what I will call the brake drum type using motor cores but not using the slots. They are a radial design with outer rotating magnets and the coils are stuck on the smooth laminated iron surface. Air gap single rotor in effect. The magnet requirement is between dual rotor and slotted core, they don't cog, the iron loss is much less than slotted cores, they are not reactance limited and with the coils stuck to an iron core the cooling is better and you can do a 2 layer winding with plenty of room for the ends and a single coil thickness in the gap.
They do need machining of the magnet drum, it is hopeless trying to find ready made things the right size.
I like the dual rotor axial design for its absolute simplicity and the main criticism of stator heating can be solved with converters to match the voltage.
If I was forced to avoid any form of electronic conversion then I would probably fall back on the drum type radial but I have no objection to machining.
For heating use there is a strong case for conventional radial with slotted cores, but they are difficult to design, an absolute pain to insert the rotor or remove it and I don't like magnets exposed to centrifugal force.
As I have often said there is no perfect design and efficiency is a term that has little meaning. Without electronics if you make the efficiency over 80% it will stall and be crap. If you want maximum efficiency in minimal winds then go axial dual rotor or radial drum if you can build it. If you can stand a bit of iron loss want cheap magnets and are willing to scrounge motor cores then go for a radial motor conversion.
Flux
